1. Field of the Invention
This invention relates to a keyboard device for an electronic keyboard instrument, such as an electronic piano, which is provided with a key switch for detecting key depression information on each key.
2. Description of the Related Art
Conventionally, there has been proposed a keyboard device of the above-mentioned type e.g. in Japanese Laid-Open Utility Model Publication (Kokai) No. H04-46493.
The keyboard device has a plurality of keys, a plurality of hammers, and a key switch each mounted on a chassis. Each key extends in the front-rear direction and has a rear end thereof pivotally supported on the chassis. Each hammer is disposed below an associated one of the keys and has a front portion thereof pivotally supported on the chassis. The key is in contact with the front end of the associated hammer from above. Further, the hammer has an upwardly protruding pressure-applying portion integrally formed therewith at a location close to the center thereof, and the pressure-applying portion has an upper surface thereof formed as a flat pressure-applying surface.
The key switch comprises a substrate and a plurality of switch bodies, and is disposed above the hammers. The substrate, which is screwed to the chassis, extends horizontally in the left-right direction. Further, first and second fixed contacts are attached to the lower surface of the substrate at respective locations close to and remote from an associated one of hammer supports, in a manner spaced from each other by a predetermined distance in the front-rear direction. Each switch body is formed as a hollow member of an elastic material, such as rubber, and is disposed on the substrate in a manner covering the first and second fixed contacts. The switch body has a flat lower surface (hereinafter referred to as “the pressure-receiving surface”) disposed substantially parallel to the lower surface of the substrate in a manner opposed to the pressure-applying surface of the hammer from above. Further, the switch body is provided with a first movable contact and a second movable contact. The first movable contact and the second movable contact are opposed to the respective first and second fixed contacts, and the distance between the second movable contact and the second fixed contact is slightly larger than that between the first movable contact and the first fixed contact.
With this construction, when the key is depressed, the front end of the hammer is pressed by the key, whereby the hammer pivotally moves to press the switch body by the pressure-applying portion. As a consequence, the first movable contact of the switch body is brought into contact with the first fixed contact, and then the second movable contact of the switch body is brought into contact with the second fixed contact, whereby detection signals indicative of the respective contact states are output. Based on the detection signals and a time lag between the two detection signals, key depression information including information on depression or non-depression of the key, key depression speed of the same, etc. is detected.
However, according to the conventional keyboard device, there is a fear that the key depression information cannot be accurately detected for the following reason: FIGS. 5A to 5C schematically show the positional relationship between the hammer 62 and the switch body 63 of the conventional keyboard device 61 and the operating state of the switch body 63. In a key-released state shown in FIG. 5A, the pressure-receiving surface 63a of the switch body 63 is positioned substantially parallel to the lower surface of the substrate 65 as described hereinbefore, whereas the pressure-applying surface 62a of the hammer 62 is rearwardly and downwardly inclined. When the key (not shown) is depressed in this state, the hammer 62 is brought into contact with the pressure-receiving surface 63a of the switch body 63 via the pressure-applying surface 62a to press and compress the switch body 63. When the amount of pivotal motion of the hammer 62 is small as shown in FIG. 5B, the whole switch body 63 is compressed by a substantially uniform degree of compression.
In general, to make a touch feeling provided by an electronic keyboard instrument more similar to a touch feeling provided by an acoustic piano, it is necessary to pivotally move the hammer through somewhat larger rotational angle. Therefore, it is desirable to make the amount of pivotal motion of the hammer 62 larger than that of the conventional hammers. However, if the amount of pivotal motion of the hammer 62 is further increased, the switch body 63 is compressed by a larger degree on a side toward the second movable contact 63c remote from the hammer support of the hammer 62 than on a side toward the first movable contact 63b, as shown in FIG. 5C, due to differences in the distance from the hammer support of the hammer 62 and the pivotal stroke of the hammer 62. This non-uniform compression of the switch body 63 causes the whole switch body 63 to be inclined mainly about the second movable contact 63c. Therefore, there is a fear that the movable contacts 63b and 63c are displaced or detached from the respective fixed contacts 64a and 64b after being brought into contact with these, thereby making unstable the contact states between the movable contacts 63b and 63c and the fixed contacts 64a and 64b, which brings about the fear that the key depression information cannot be accurately detected.